1. Field of the Invention
This invention relates to a method for positioning masks, reticles, wafers, and so on for production of semiconductor devices. More particularly, it is concerned with a positioning method adapted for use with a wafer prober and a wafer scriber.
2. Description of the Prior Art
As a system for automatically detecting a wafer position using a laser or a high brightness light source, there has been known one, in which a linearly converged laser spot irradiates wafer street lines and the scattered light above is photo-electrically detected. According to this known system, when the irradiated wafer street lines are totally reflecting surfaces, the photo-electric signal is approximate to zero. When the laser spot is on the circuit pattern, the scattering phenomenon becomes substantial and the photo-electric signal is detected with high intensity. Therefore, in utilization of the above-mentioned properties, the laser beam is oscillated with a predetermined amplitude, and a time interval where the photo-electric signal becomes substantially zero is measured, thereby detecting the wafer street lines.
In case, however, the street lines are of multi-layered structure, and the scattered light from the street lines has complicated intensities, or the street lines are perfectly non-existent in the wafer, the zero interval of the photo-electric signal cannot be measured; hence no position detection can be done.